The invention relates to a coating process for coating a glass substrate and especially to a coating process for coating surface of a glass substrate in normal air pressure according to the preamble of claim 1. The present invention further relates to a coating apparatus for coating a glass substrate and especially to a coating apparatus for providing a coating on a surface of a glass substrate in normal air pressure according to the preamble of claim 14.
It is generally know to use liquid starting materials for coating glass by atomizing the liquid starting materials into droplets and directing the formed droplets on the surface of glass to be coated for producing a coating. In other words according to the prior art the droplets are brought to the surface of the substrate to be coated as liquid droplets, whereby the coating is formed on the surface of the substrate such that first the droplets brought on the surface are pyrolized or the vaporizable substances of the droplets are vaporized for providing a coating on the surface of the substrate.
The problem in the above identified prior art coating process is the slow growth rate of the coating, which is due to fact that the liquid droplets brought to the surface of the glass produce a liquid film on the surface of the glass. The pyrolization and vaporization of the liquid film is slow. The slow growth rate limits the utilization of this coating process in many applications such as when a coating is produced on a moving sheet glass. Furthermore, the uniformity of the produced coating is difficult to control in this prior art coating process.
U.S. Pat. No. 4,735,861, Ford Motor Company, Apr. 5, 1988, describes the production of a gray colour coating on a glass substrate. The coating is formed by formulating a solution of dissolved metal compounds, in a solvent therefor which will volatilize in the presence of heat and oxygen thereby permitting the metals to react with oxygen to develop a multimetal oxide coating adherent to the glass surface. The solution is sprayed on the glass surface. The metals are oxideized and part of the metal oxides so-developed become adherent to the surface of the glass substrate to form a film thereon. The coating formation is thus based on the deposition of metal oxide particles, not on surface reactions.
An other prior art method for providing a coating on a glass substrate is to use known vapour deposition methods such as CVD (chemical vapour deposition). In these conventional vapour deposition methods the surface of the glass substrate to be coated is subjected to vapour starting materials which react with the surface of the glass or with each other to form a coating on the surface of the glass.
The problem with these conventional prior art vapour deposition methods is that the staring materials are vaporized distant from the surface of the substrate to be coated and the vaporized starting materials are transported with a carrier gas to the substrate. The long transportation distance of the vaporized starting materials causes undesirable particle formation during the transportation of the vaporized starting materials. The undesirably formed particles end up to the surface of the substrate to be coated and therefore reduce the quality of the produced coating.